Android 5 screen pinning for kiosks

When I first heard about screen pinning in Lollipop, I though it would be perfect for making low-cost kiosks that use dedicated apps.

Here is the scenario I imagined: The admin would configure the device, then pin the app to be used. The user would be locked into using only the pinned app, and would not be able to lock themselves out of the device.

Each of the individual system buttons (back, home, overview) are disabled. Perfect. Pressing the back button gives instructions on how to exit the pinned app (hold back+overview).

It works well until the user tries to exit the app. Holding the back+overview buttons effectively locks the device, with no way to return to the app.

Also, the user is still allowed to power off the device while an app is pinned. Why?!

In conclusion...

Is there an out-of-the-box way of making a screen pinned app that will be feasible to use as a kiosk app?

Or do I need to take a programmatic approach and use something like Device Owner?